Method for processing detection signal of vibratory inertial force sensor and vibratory inertial force sensor

ABSTRACT

A method for processing a detection signal of a vibratory inertial force sensor is disclosed. This method improves detection accuracy of the vibratory inertial force sensor. A detection circuit of the vibratory inertial force sensor removes harmonic component from signals synchronously wave-detected, and amplifies the resultant signals, and then smoothes the amplified signals. A vibratory inertial force sensor adopting this method is also disclosed.

TECHNICAL FIELD

The present invention relates to a method for processing a detectionsignal of vibratory inertial force sensor, and it also relates to avibratory inertial force sensor adopting the same method.

BACKGROUND ART

FIG. 6 shows a block diagram of a vibratory angular velocity sensor, oneof conventional vibratory inertial force sensors, and the vibratoryangular velocity sensor comprises the following elements:

-   -   sensor element 203 including driver section 201 and sensor        section 202;    -   drive control circuit 204 for applying a control voltage to        driver section 201, thereby vibrating sensor element 203, and        then controlling the vibration; and    -   detection circuit 205 for processing a detection signal supplied        from sensor section 202.

In detection circuit 205, the detection signal supplied from sensorsection 202 is differentially amplified by differential amplifier 206.The amplified signal and an inverted signal of the detection signalinverted by inverting amplifier 207 are synchronously wave-detected bysynchronous wave detector 208. Then the resultant signal is smoothed bylow-pass filter 209, so that the signal with disturbance noise, such asexternal impact, suppressed is output.

Conventional low-pass filter 209 firstly amplifies the signal havingundergone the synchronous wave-detection with inverting amplifier 220working as a pre-amplifier, then smoothes the resultant signal withsmoothing circuit 221, or the signal is amplified and smoothed at thesame time by an active filter (not shown).

The foregoing conventional vibratory inertial force sensor is disclosedin, e.g. Unexamined Japanese Patent Publication No. 2002-267448.

The signal having undergone the synchronous wave-detection in wavedetector 208 of conventional vibratory inertial force sensor; however,draws a saw-tooth waveform as drawn by synchronous wave-detection output208 a shown in FIG. 7. At switchover section 210 of this waveform, theamplifying capacity of inversing amplifier 220 or the active filterworking as a pre-amplifier of the low-pass filter cannot fully track thesaw-tooth waveform, so that the waveform actually drawn by output 220 afrom the inversing amplifier becomes as shown in FIG. 7. In FIG. 7, thehorizontal axis represents a time, and the vertical axis represents anelectrical potential of respective output signals.

As shown in FIG. 7, output 220 a supplied from the inverting amplifierand having undergone the amplification includes waveform error 212 whichcauses offset 211 at sensor output 205 a having undergone the smoothing.Smoothing circuit 221 of low-pass filter 209 thus cannot implement anaccurate smoothing process, so that the performance of the vibratoryinertial force sensor is obliged to lower due to internal process withindetection circuit 205.

DISCLOSURE OF INVENTION

The present invention addresses the problem discussed above, and aims toprovide a method for improving detection accuracy in processing adetection signal of vibratory inertial force sensor, and it also aims toprovide a vibratory inertial force sensor adopting the same method.

To achieve this objective, the present invention adopts the followingmethod: in a detection circuit, among others, of the vibratory inertialforce sensor, a signal having undergone the synchronous detection isremoved harmonic component, and the resultant signal is amplified andthen smoothed. Use of this method allows improving detection accuracy ofthe vibratory inertial force sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a vibratory inertial force sensor inaccordance with an exemplary embodiment of the present invention.

FIG. 2 shows a top view of a sensor element to be used in the vibratoryinertial force sensor.

FIG. 3 shows transition of waveforms detected by the vibratory inertialforce sensor.

FIG. 4 shows transition of waveforms detected by the vibratory inertialforce sensor and processed after synchronous wave-detection.

FIG. 5 schematically illustrates waveform components after thesynchronous wave-detection.

FIG. 6 shows a block diagram of a vibratory angular velocity sensor asan example of a conventional vibratory inertial force sensor.

FIG. 7 shows transition of a waveform after the synchronous detection inthe conventional vibratory inertial force sensor.

DESCRIPTION OF REFERENCE MARKS

-   -   101 driver section    -   102 sensor section    -   103 sensor element    -   104 drive control circuit    -   105 detection circuit    -   114 drive arm    -   115 monitor

PREFERRED EMBODIMENT OF THE INVENTION

An exemplary embodiment of the present invention is demonstratedhereinafter with reference to the accompanying drawings. FIG. 1 shows ablock diagram of a vibratory angular velocity sensor as an example of avibratory inertial force sensor of the present invention. This vibratoryangular velocity sensor basically comprises the following elements:

-   -   sensor element 103;    -   drive control circuit 104 for controlling the vibration of        sensor element 103; and    -   detection circuit 105 for processing a signal supplied from        sensor element 103.

FIG. 2 shows a top view detailing the structure of sensor element 103 tobe used in the vibratory angular velocity sensor of the presentinvention. As shown in FIG. 2, sensor element 103 comprises thefollowing elements:

-   -   fork oscillator 113 made from silicone substrate;    -   a pair of drive arms 114 extending from fork oscillator 113;    -   drive electrodes 101 a working as driver section 101 formed of        piezoelectric thin film made from PZT (lead zirconium titante)        sandwiched by electrodes 101 a at its upper and lower faces and        disposed on arms 114;    -   sensor electrodes 102 a working as sensor section 102 and        disposed on arms 114; and    -   monitor electrodes 116 a formed by sandwiching the piezoelectric        thin film made from PZT at the upper and the lower faces with        electrodes 115 a and coupled to monitor 115.

Drive control circuit 104 shown in FIG. 1 applies a drive power to driveelectrodes 101 a, thereby vibrating drive arms 114 to both sides asarrow marks 116 show. In this vibration state, an angular velocityaround the sensing axis is applied to arms 114, so that drive arms 114deflect along back and forth direction in FIG. 2 due to Coriolis force.The deflection allows sensor electrodes 102 a to output a detectionsignal to detection circuit 105 shown in FIG. 1.

A drive power applied from drive control circuit 104 to drive electrode101 a is adjusted so as to accomplish the following performance: Eachone of monitor electrodes 115 a shown in FIG. 2 senses an amount ofamplitude of drive arms 114, and feeds back this information to drivecontrol circuit 104 via monitor 115, so that the amount of amplitudebecomes a specified state.

FIG. 3 shows transition of waveforms of respective signals in thevibratory angular velocity sensor in accordance with this embodiment. InFIG. 3, the horizontal axis represents a time, and the vertical axisrepresents an electric potential of respective signals. FIGS. 4 and 5use the same system as FIG. 3.

In detection circuit 105 shown in FIG. 1, detection signals (sensedoutputs 102 b, 102 c shown in FIG. 3) supplied from two sensorelectrodes 102 a disposed at sensor element 103 are amplified byamplifier 110 formed of a current amplifier or a charge amplifier. Thenthe two amplified signals are differentially amplified by differentialamplifier 106, and the resultant signals are delayed their phase by 90degrees by phase shifter 117 with respect to these resultant signals(output 106 a from the differential amplifier shown in FIG. 3) havingundergone the differential amplification. The phase-delayed signal(output 117 a from the phase shifter shown in FIG. 3) is branched, and afirst branched signal is fed directly into synchronous detector 108, anda second branched signal is reversed the phase by inverting amplifier107 before the resultant signal (output 107 a from the invertingamplifier shown in FIG. 3) is fed into synchronous wave detector 108.

Wave detector clock section 118 converts monitor signal 115 b suppliedfrom monitor 115 into wave-detection CLK output 118 a drawing a pulsewaveform (an output from the wave detector clock section) shown in FIG.3. Then in synchronous wave detector 108, those two input signals(output 117 a from the phase shifter and output 107 a from the invertingamplifier shown in FIG. 3) are wave-detected by output 118 a from wavedetector clock section 118, thereby forming synchronous wave detectionoutput 108 a drawing a saw-tooth waveform shown in FIG. 3.

This vibratory angular velocity sensor has low-pass filter 109 shown inFIG. 1 and which filter 109 smoothes saw-tooth synchronouswave-detection output 108 a. Low-pass filter 109 works in the followingmanner: synchronous wave-detection output 108 a undergoes passive filter119 for removing the harmonic component, then is smoothed by smoothingcircuit 121 such as an integrator. This mechanism allows suppressing areduction in detection accuracy of detection circuit 105 comparing withthe conventional one shown in FIG. 7, where synchronous wave-detectionoutput 208 a is firstly amplified, and then smoothed. As a result, thedetection accuracy of the vibratory inertial force sensor can beimproved. In the meantime, the passive filter discussed above is afilter formed of passive components only, such as capacitors, resistorsand so on.

To be more specific, the conventional pre-amplifier or active filterfirstly amplifies and then smoothes synchronous wave-detection output208 a, i.e. saw-tooth shaped output 208 a is amplified by the pre-amp orthe active filter, thereby incurring time lag 210 a at a switchoversection of the waveform due to the poor tracking ability of theamplifier. As a result, waveform error 212 is generated between anactual waveform and the amplified waveform. The actual waveform witherror 212 is smoothed, thereby producing offset 211 in the output.

However, synchronous wave-detection output 108 a or 208 a supplied fromsynchronous wave detector 108 shown in FIG. 1 or wave detector 208 shownin FIG. 6 includes secondary harmonic component 219 b and tertiaryharmonic component 219 c on top of fundamental harmonic component 219 ashown in FIG. 5. Therefore, as shown in FIG. 4, synchronouswave-detection output 108 a is fed into passive filter 119 for removingthe harmonic component, and then the resultant output 119 a is supplied,which output 119 a contains only sine-wave like moderately curvedfundamental component 219 a. This output 119 a supplied from passivefilter 119 is amplified by amplifier 120, and the resultant output 120 ais smoothed by smoothing circuit 121. The foregoing process allows theoutput from the vibratory angular velocity sensor to become sensoroutput 105 a as shown in FIG. 4, which output 105 a includes no waveformerror 212 shown in FIG. 6, so that the production of offset 211 can besuppressed. As a result, the reduction in detection accuracy ofdetection circuit 105 can be suppressed, and improvement in thedetection accuracy of the vibratory inertial force sensor can beexpected.

Passive filter 119 that removes harmonic component from detectionsignals has the following structure although not shown in a drawingspecifically: resistors in series with respect to a path of thedetection signal, and a capacitor is placed between at least one end ofthe resistors and a reference electric potential. In other words, atypical harmonic suppressing circuit can work as passive filter 119.

In the foregoing embodiment, the vibratory angular velocity sensor istaken as an example of the vibratory inertial force sensor; however, thepresent invention is not limited to this example. Any structure thatsenses inertial force, such as acceleration, by vibrating the drive armcan produce a similar advantage to what is discussed previously.

INDUSTRIAL APPLICABILITY

The present invention allows a vibratory inertial force sensor toachieve higher detection accuracy, so that it is useful for electronicapparatuses requiring a highly accurate sensor of inertial force amongothers. The present invention is thus well applicable to the industrialuse.

1. A method for processing a detection signal of vibratory inertialforce sensor, which sensor comprises: a drive arm; a driver disposed tothe drive arm for vibrating the drive arm; a sensor section forgenerating a detection signal through deflection produced by inertialforce applied to the drive arm; a monitor for monitoring the vibrationof the drive arm; a drive control circuit for controlling an amount ofvibration of the drive arm; and a detection circuit for processing thedetection signal, the method, to be implemented in the detectioncircuit, comprising the steps of: differentially amplifying twodetection signals detected by the sensor section and having a phasedifference of 180 degrees; synchronously wave-detecting thedifferentially amplified signals with a monitor signal supplied from themonitor; removing harmonic component from the signals synchronouslywave-detected; amplifying the signals from which the harmonic componentis removed; and then smoothing the amplified signals.
 2. A vibratoryinertial force sensor comprising: a drive arm; a driver disposed to thedrive arm for vibrating the drive arm; a sensor section for generating adetection signal through deflection produced by inertial force appliedto the drive arm; a monitor for monitoring the vibration of the drivearm; a drive control circuit for controlling an amount of vibration ofthe drive arm; and a detection circuit for processing the detectionsignal, wherein, the detection circuit differentially amplifies twodetection signals detected by the sensor section and having a phasedifference of 180 degrees, and synchronously wave-detects thedifferentially amplified signals with a monitor signal supplied from themonitor, removes harmonic component from the signals synchronouslywave-detected, amplifies the signals from which the harmonic componentis removed, and then smoothes the amplified signals.